The use of inkjet printing systems in offices and homes has grown dramatically in recent years. The growth can be attributed to drastic reductions in cost of inkjet printers and substantial improvements in print resolution and overall print quality. While the print quality has drastically improved, research and development efforts continue toward improving the permanence of inkjet images because this property still falls short of the permanence produced by other printing and photographic techniques. A continued demand in inkjet printing has resulted in the need to produce images of high quality, high permanence, and high durability, while maintaining a reasonable cost.
In inkjet printing, the inkjet image is formed on a print medium when a precise pattern of dots is ejected from a drop-generating device known as a printhead. The typical inkjet printhead has an array of precisely formed nozzles located on a nozzle plate and attached to an inkjet printhead array. The inkjet printhead array incorporates an array of firing chambers that receive liquid ink, which includes pigment-based inks and/or dye-based inks dissolved or dispersed in a liquid vehicle, through fluid communication with one or more ink reservoirs. Each chamber has a thin-film resistor, known as a firing resistor, located opposite the nozzle so ink can collect between the firing resistor and the nozzle. Upon energizing of a particular firing resistor, a droplet of ink is expelled through the nozzle toward the print medium to produce the image.
Print media have different surface energies. In addition, the surface energies are not uniform on the same print medium. Non-coated plain paper print media have paper fibers, fillers, and wet strength resins, and various sizing, all of which have a different amount of affinity for water-based inks. The surfaces of the print medium are mostly hydrophilic on areas where fibers and fillers are exposed and are hydrophobic in areas where wet strength resins are exposed. In general, print media have more hydrophilic sites than the hydrophobic sites on paper. This causes the inkjet drop to experience different interfacial surface energies not only from print medium to print medium but also on the same print medium.
With self-dispersed pigment inks, conventional approaches to ink design with a solvent, surfactant, and water do not work because they do not provide enough energy configurations to pacify the print medium to make it uniform.